Field of the Invention
The present invention relates to a technology for stably discharging paper sheets remaining in an apparatus due to a trouble such as a paper jam in an image forming apparatus, an image forming system in which other apparatuses are connected to an image forming apparatus, and an image formation control program for controlling an image forming apparatus and an image forming system.
Description of the Related Art
In an image forming apparatus such as a printer or a copying machine, feeder trays that store paper sheets of more than one type are provided so as to cope with various printing conditions.
There exists another type of image forming apparatus that reverses and circulates a paper sheet having an image formed on a first image thereof, and then re-supplies the paper sheet to the image forming unit, so as to form images on both sides of the paper sheet.
In a case where a paper jam occurs at a site in an image forming apparatus, the operation of the image forming apparatus is stopped, the user removes the trouble-causing paper sheet that has caused the paper jam, and the paper sheets (troubled paper sheets) still remaining in the image forming apparatus are gathered onto a single discharge tray and are automatically discharged through a purging process.
JP 62-85261 A, JP 07-215530 A, and JP 2000-095389 A disclose various suggestions for handling troubled paper sheets when a paper jam occurs.
JP 62-85261 A discloses a technique by which troubled paper sheets are detected by a sensor after the trouble-causing paper sheet is removed, and a purging process is then automatically performed.
JP 07-215530 A discloses a process of activating a timer every time a sensor detects a paper sheet during a purging process, and determining the purging process to have been completed if there is no detection notification over a certain period of time.
JP 2000-095389 A discloses a technique by which conveyance drive motors provided in respective conveyance paths are activated at different times in a purging process so as to prevent collisions between paper sheets in an apparatus having junctions between the paper sheet conveyance paths.
Where the conveyance speed of a paper sheet at the time of the transfer of a toner image onto the paper sheet in the image forming unit is the process conveyance speed in an image forming apparatus, there is a known conveyance control method by which a paper sheet from a sheet feeding unit is conveyed to the site in front of the image forming unit at a sheet conveyance speed that is higher than the process conveyance speed.
Even if the sheet feeding slightly delays as the paper slips while being conveyed, the delay time can be absorbed by a temporary halt in front of the image forming unit by using this conveyance control method, and the image formation intervals can be made uniform to secure productivity.
Also, not only in a case where paper sheets are successively conveyed from the same feeder tray but also in a case where feeder trays are switched while image formation is being performed, reduction in productivity can be avoided or minimized, as the sheet conveyance speed is higher than the process conveyance speed.
In such an image forming apparatus, a paper sheet is conveyed from a feeder tray to the site (the position of resist rollers) in front of the image forming unit at the sheet conveyance speed, and is conveyed from the resist rollers at the process conveyance speed. Image formation is then performed.
There are cases where the bottom edge of a paper sheet of a certain paper size is still held between rollers of the sheet feeding unit when the resist rollers are rotated. In such a case where the bottom edge of a paper sheet is still held between rollers of the sheet feeding unit when the paper sheet is moved by the resist rollers, rollers of the sheet feeding unit are made to rotate by a clutch mechanism, to convey the paper sheet at the process conveyance speed.
In such a situation, however, the clutch mechanism of the rollers of the sheet feeding unit might be switched on so as to start conveyance of the next paper sheet from a feeder tray. As a result, the bottom edge of the paper sheet being conveyed by the resist rollers is held between the rollers of the sheet feeding unit, and the bottom edge of the paper sheet is conveyed at the sheet conveyance speed. Although the top edge of the paper sheet is being conveyed by the resist rollers at the process conveyance speed, the bottom edge of the paper sheet is pushed from the bottom at the sheet conveyance speed that is higher than the process conveyance speed. As a result, the paper sheet might be folded or crumpled, to cause a paper jam.
In an image forming apparatus in such a state, the trouble-causing paper sheet is removed after the occurrence of the paper jam, and the troubled paper sheets remaining in the apparatus are then discharged through a purging process. In that case, the paper sheet needs to be conveyed in the same manner as those in a regular image forming operation.
After the occurrence of the paper jam, the remaining paper sheets are still moving through the inertia of the conveyance rollers. Furthermore, due to the trouble-causing paper sheet removing operation performed by the user, the paper sheet state might differ from that at the time of the occurrence of the jam.
Therefore, in a case where the same paper sheet conveyance as that in a regular image forming operation is performed for a purging process, the paper in the sheet feeding unit is pushed into the image forming unit due to the above described difference between the process conveyance speed and the sheet conveyance speed, for example, and might cause another paper jam. In an image forming system in which a sheet feeding apparatus is connected to an image forming apparatus, the same problem as above might be caused.
Such a problem cannot be solved by any of the techniques disclosed in the above mentioned patent documents, and has not been recognized as a problem that should be solved.